中国聚变工程实验堆(China Fusion Engineering Test Reactor,CFETR)负离子源中性束系统(Negative ion based Neutral Beam Injection system,NNBI)验证样机拟引出负氢离子束.离子束在产生和传输过程中,束粒子与样机结构材料固体靶相互碰撞,将产生韧致辐射(X射线),当CFETR NNBI验证样机运行在设计的参数下(束能量为200 keV,流强20 A),距离离子源真空壁(真空壁厚2 cm)1 m处的壁外剂量率高于一般工作人员辐射剂量率限值(10 μSv?h?1).为了降低辐射剂量率,确保工作人员辐射安全,本文通过对样机进行辐射屏蔽理论计算与模拟研究,提出了将样机下沉加铅板的屏蔽设计方案,并开展了辐射模拟分析.结果表明:该方案满足CFETR NNBI验证样机运行的辐射安全要求.
[Background] China fusion engineering test reactor (CFETR) negative ion based neutral beam injection system (NNBI) prototype was designed for hydrogen beam operation. When the NNBI prototype works, the energetic particles collide with the solid targets of the prototype structural material during production and transmission to produce bremsstrahlung. When the CFETR NNBI prototype is designed to operate with a beam energy of 200 keV and beam current of 20 A, the dose rate outside the vacuum wall is higher than the limit dose rates of general worker radiation (10 μSv?h?1). [Purpose] This study aims to reduce the radiation dose rate of the CFETR NNBI with hydrogen beam energy of 200 keV. [Methods] The radiation dose of the prototype was simulated by the radiation shielding theory. The shielding design scheme of sinking the prototype with lead plate was put forward and evaluated. [Results] When the CFETR NNBI is placed underground and shielding layer on the top, the outside dose rate at 1 m from vacuum wall (with 2 cm thickness) of ion source (200 keV, 20 A) is below the limit. [Conclusion] The design scheme can meet the radiation safety standards when the CFETR NNBI prototype operated with radiation shielding.